May 23, 1889] 



NATURE 



n 



(B) They have also a great value on account of the actual 



:ts of natural history and physiology which they record. 



(C) They have, thirdly, a quite distinct and perhaps 

 their most definite interest in their relation to psychology. 



It seems, indeed, that the most interesting problems 

 which are brought before us in the Muybridge photographs 

 of the galloping horse are not so much those of animal 

 locomotion itself as these, viz. how is it that this (which 

 is demonstrated by the photograph to be the actual series 

 of attitudes assumed by the galloping horse) has given 

 rise through the human eye and brain to the conventional 

 representation with outstretched fore and hind legs 1 Can 

 the conventional representation be justified? If it can- 

 not, what do we really see as opposed to what really is ? 

 What is the objective fact — the brain-picture — as opposed 

 to the objective fact — the sun-picture ? for it is the former 

 which the painter struggles to reproduce. Here, in fact, 

 science and art are absolutely united in one common 

 search after truth.^ On this subject I hope to say more 

 in a subsequent article. 



With regard to the method and apparatus employed by 

 Mr. Muybridge in the present series of photographs, it is 

 to be noted that they are different from those employed 

 in 1878-79. As in his earlier photographs, so in the 

 later series, Mr. Muybridge's object was to obtain suc- 

 cessive clear and separate pictures. In this respect his 

 method differs altogether from the simpler and much 

 cheaper one used by Marey since the publication of 

 Muybridge's first results. Marey's method is, no doubt, 

 •efficient, and in a certain sense sufficient, for the purpose 

 of determining some of the main facts as to the phases 

 of the limbs in locomotion. The object to be studied 

 moves in sunlight before a dark background. A photo- 

 graphic camera faces it. A large disk with one or more 

 openings in it is rapidly revolved in front of the lens. 

 Whilst the opening is passing the lens, the moving object 

 is photographed ; then there is darkness in the camera 

 until an opening again passes the lens. The moving 

 object has now a new position, and is photographed anew 

 on the same plate : and so on, again and again, as often as 

 required, or until the object has moved beyond the range 

 of the plate. Thus on the same plate are developed a 

 series of images, readily compared and faithfully depict- 

 ing phases of the movement studied at definite intervals 

 of time. The advantage of this method consists in the 

 simplicity of the apparatus required ; its defect is that 

 with rapidly moving objects the amount of light neces- 

 sary is not easily obtained together with a sufficiently 

 dark background. 



Mr, Muybridge's perfected apparatus consists of three 

 batteries, each of twelve (or more) cameras. One battery 

 is parallel to the track, a second looks up it from behind 

 the moving object, a third faces the moving object. Each 

 camera is provided with a specially contrived "exposer" 

 or shutter (so called) which is "let off" by means of an 

 electric current. The exposure thus given is as small as 

 the 1/5000 of a second. The electric connection is such 

 that in each of the batteries A, B, C, a camera, Ar, is 

 exposed absolutely synchronously with cameras Bi and 

 Ci. So, too, with regard to cameras A2 B2, and C2, and 

 with the rest up to A12, B12, and C12. Each exposure 

 thus gives a group of three synchronous pictures record- 

 ing lateral, fore, and hind views of the moving object. 

 The intervals between the exposures of the successive 

 trios of cameras, ABCi, ABC2, ABC3, &c., is determined 

 by the rotation of a wheel carrying a metallic brush in 

 front of a circular plate, on the circumference of which 

 are placed equidistant metal studs, one connected with 

 the wires going to each trio. The circuit is completed by 



• Mr. Francis Gallon, in Nature, vol. xxv!. p. 228, has made a valuable 

 suggestion on this subject — which is repeated by Mr. George Snell in the 

 Century \n \%'i,-y—\.o \\xi effect that the brain-picture consists of a blending 

 of the extreme positions of extensi )n of the hind Kmbs and the fore limbs, 

 which, although not actually coincident in time, are Lngest in duration of 

 all the phases passed through. 



the contact of the metal studs with the moving metallic 

 brush. The wheel can, by a special mechanism, be 

 rotated so that a revolution is effected in one second Or 

 in any fraction of a second. During one revolution the 

 twelve studs make contact at equal intervals of time, and 

 twelve groups of three photographs each, exposed for the 

 1/5000 of a second and separated from one another by 

 one-twelfth of the time occupied by a revolution, are 

 taken. Usually, Mr. Muybridge found it convenient to 

 set the wheel so that it should rotate at such a rate as to 

 give 1/30 of a second between the contact of the twelve 

 studs, but longer intervals were also employed. Behind 

 the track along which the object was made to move was 

 a black screen divided by white threads into squares of 

 about 2 inches to the side. The bright sunlight of the 

 open space was the illuminating agent, no artificial light 

 being sufficiently powerful. A full account of the appa- 

 ratus will be found by those specially interested in the 

 subject in a book published by Lippincott Company of 

 Philadelphia in 1888, entitled " The Muybridge Work at 

 the University of Pennsylvania — the Method and the 

 Result." Enough has been said here to give an idea of 

 the perfection attained in the apparatus. 



With regard to the results, in the form of facts recorded 

 of interest to the naturalist and physiologist, it is not 

 easy to speak in the brief space at my disposal. The 

 branch of inquiry opened out by this method of instan- 

 taneous photography is in its infancy, and generalizations 

 of any consequence can hardly be looked for at present. 

 The questions to be answered — the hypotheses which it 

 will be necessary to test— have not yet been formulated. 

 What we have in Mr. Muybridge's published plates is a 

 number of individual studies. By far the most comple^e 

 investigation is that of the various gaits of the horse, 

 which may be considered as very nearly exhaustive. An 

 interesting generalization which perhaps might have been 

 arrived at without the aid of the camera —but could not 

 have been clearly demonstrated without it — is that the 

 walking gait of all Mammalia is the same, including the 

 quadrupedal crawl of the infant man, and the progression 

 of the sloth as it hangs from a horizontal pole. An 

 apparent exception to this rule is found in the baboon, 

 which instead of extending one pair of "diagonals"^ 

 simultaneously and then bringing them together beneath 

 the body whilst the other pair is extended, exhibits the 

 simultaneous extension of a lateral pair followed by their 

 approximation whilst the opposite lateral pair are ex- 

 tended. The analysis of various gaits involves many 

 points besides the mere swing of the limbs, the 'most 

 obvious and important of which are the succession of the 

 footfalls, the weight of impact, and its exact period (which 

 need not coincide with visible contact of foot and ground), 

 the exact mechanical value of the complex stroke given 

 by the limb, and the exact period at which it is applied 

 (which need not altogether coincide with that part of it given 

 by the foot as it leaves the ground). Another factor to be 

 studied is the rotation of the various segments of the limb. 



Information and suggestion on these points are fur- 

 nished by the photographs, but it is by no means to be 

 supposed that it is possible that once for all these prob- 

 lems can be settled by any set of photographs, however 

 elaborate. The turning of the quill-feathers of the bird's 

 wing during the upward movement or recovery of the 

 wing, so that they cut the air instead of pressing it with a 

 broad surface, is one of the prettiest demonstrations 

 which Mr. Muybridge has obtained. That such a move- 

 ment takes place seems to have been observed by the 

 ordinary man in the remote past, for the word " feather- 

 ing,'' applied to the similar movement of an oar in rowing, 

 implies a knowledge of the setting of the feathers in the 

 upward movement of the bird's wing. 



' The "diagcnals" are the right fore hmband the left hind limb, and the 

 left fore limb and the righ t hind Umb ; the "' laterals " are the right fore and 

 hind limbs and the left Lre and hind limbs. 



